Photolithography has hitherto been used for manufacturing semiconductor devices. However, with miniaturization of the semiconductor devices, photolithography is becoming insufficient in resolving power, and pattern formation is thus becoming difficult. Hence, nanoimprinting has recently come to be used in place of photolithography.
In nanoimprinting, concavities and convexities are formed by selectively removing the surface of a quartz substrate, a pattern (device pattern) obtained by inverting a resist pattern desired to be formed, and an alignment mark for alignment are formed, and thus an imprint mask is produced. Then, an ultraviolet cure resist material is applied on the substrate to be processed, and the imprint mask is pressed onto this resist material. Next, while the imprint mask is held pressed, the resist material is irradiated with ultraviolet rays through the imprint mask, to be cured. In this manner, the device pattern formed in the imprint mask is transferred to the resist material, to form the resist pattern. In nanoimprinting, since there are fewer factors of variations in focus depth, aberration, exposure, and the like which have been problems with conventional photolithography, once one imprint mask is produced, a large number of resist patterns can be formed in an extremely simple and accurate manner.
Incidentally, manufacturing of the semiconductor device includes a process of forming a new pattern on a substrate previously formed with a pattern. In the case of using nanoimprinting for such a process, it is necessary to perform alignment of the imprint mask with respect to the substrate with high accuracy. This alignment is performed by overlapping an alignment mark formed in the imprint mask on an alignment mark formed on the substrate, while observing the marks with visible light.
However, since a refractive index of quartz as the material for the imprint mask with respect to the visible light is almost equivalent to a refractive index of the ultraviolet cure resist material with respect to the visible light, when the imprint mask is pressed onto the resist material and the resist material gets into the concave section of the alignment mark, the alignment mark becomes invisible. There has thus been a problem in that the alignment cannot be performed with sufficient accuracy.